In the processing and packaging of semiconductor devices, wire bonding continues to be the primary method of providing electrical interconnection between two locations within a package (e.g., between a die pad of a semiconductor die and a lead of a leadframe). More specifically, using a wire bonder (also known as a wire bonding machine) wire loops are formed between respective locations to be electrically interconnected. The primary methods of forming wire loops are ball bonding and wedge bonding, with ball bonding being the preferred technique. U.S. Pat. No. 5,945,065 to Kikuchi et al. illustrates conventional ball bonding and wedge bonding processes, as discussed below.
An exemplary conventional wedge bonding sequence is illustrated in FIGS. 2A-2D of U.S. Pat. No. 5,945,065, where the sequence includes: (1) arranging a wire 12 through a lower end of a wedge bonding tool 11, with an electrode 15 of an IC chip 16 below the wedge bonding tool 11; (2) bonding the wire 12 to the electrode 15 through the application of ultrasonic waves to the wedge bonding tool 11, where the wedge bonding tool 11 is pressing the wire 12 against electrode 15; (3) releasing the wire using a clamper 12, and then routing the wire to an outer lead 18, and then lowering the wire 12 to the outer lead 18; (4) bonding the wire 12 to the outer lead 18 through the application of ultrasonic waves; and (5) lifting the clamper 17 while clamping the wire 12 such that the wire 12 is cut. Unfortunately, wedge bonding has certain deficiencies in comparison to ball bonding (e.g., directional issues with the bonding head which result in a slow operation and inaccuracy problems, amongst others). These deficiencies have made ball bonding the preferred wire bonding technique.
Now referring to FIGS. 1A-1D of U.S. Pat. No. 5,945,065, an exemplary conventional ball bonding sequence includes: (1) using electric discharge to form a free air ball 4 on an end of a wire 2 extending from a capillary bonding tool 1; (2) lowering the capillary 1, and pressing the ball 4 to an electrode 5 of an IC chip 6, and applying ultrasonic waves to the ball through the capillary 1 to form a bond between the ball and the electrode 5 (where the IC chip 5 including the electrode 5 is heated by a heater block); (3) routing wire 2 (through motion of capillary 1) toward above outer lead 8, and lowering wire 2 to outer lead 8; (4) bonding the wire 2 to the outer lead 8 through the application of ultrasonic waves; and (5) cutting the wire 2 by closing and raising a damper 7. Of course, in forming the bonds between (a) the ends of the wire loop and (b) the bond site (e.g., a die pad, a lead, etc.) varying types of bonding energy may be used including, for example, ultrasonic energy, thermosonic energy, thermocompressive energy, amongst others. Other examples of ball bonding techniques are disclosed in, for example, U.S. Pat. No. 6,933,608 to Fujisawa; U.S. Pat. No. 6,815,836 to Ano et al.; U.S. Pat. No. 6,715,666 to Imai et al.; U.S. Patent Application Publication No. 2005/0072833 to Wong et al.; and U.S. Patent Application Publication No. 2005/0109819 to Qin et al.
While there are clearly numerous advantages to ball bonding (in comparison to wedge bonding), there are also disadvantages to ball bonding such as, for example: the inclusion of an electronic flame-off assembly (i.e., an EFO assembly) for forming the free air balls; complications to the ball bonding process related to the operation of the EFO assembly; and increased spacing between adjacent bonds because of the formation of the free air balls (in comparison to the wire width requirements in wedge bonding).
Thus, it would be desirable to provide improved methods of wire bonding with certain of the advantages of ball bonding and wedge bonding.